A major problem in CCD camera systems is the elimination of KTC noise, the thermal noise of the FET switch associated with a CCD reset gate and is a function of temperature (T) and capacitance (C) of the gate times a constant (K). Prior art CCD camera systems employ three types of circuits to eliminate KTC noise. The first of these is the DC Restore Circuit DCR, which samples the KTC noise at two different positions in a pixel signal and subtracts the second valise from the first value obtained, This circuit has to work with a Low Pass Filter (LPF) to limit the noise bandwith. Such a filter causes pixel feedthrough problems and requires the circuit designer to compromise between system noise and pixel feedthrough. The advantage of the CDS circuit is that it can operate at high speed and change the pixel rate on the fly.
The second type of circuit is the Dual Slope Integrator(DSI) which has the highest performance of the three types of circuits but requires the most accurate components to implement. It is impractical to implement at high pixel rates because it requires two integration operations.
The third type of circuit is the Transverse Filter (TF) which can operate at very high pixel rates and does not have the feedthrough problems. Such a filter requires an accurate high speed Differential Amplifier and precision passive delay lines for achieving acceptable performance. Further, such a filter requires very precisely controlled timing causing increased difficultly in implementation. Also, once the hardware is installed (i.e. the delays are set), the read out speed is set and impossible to change during operation. This later draw hack prevents the system from carrying a out binning operations which are important for CCD systems which do not have binning registers.
It is clear that each of the three types of prior art circuits for eliminating KTC noise has its drawbacks. A characteristic of a system employing any one of the above types of circuits is that it uses the DSI for low pixel rate and DCR or TF for high pixel rates but not both. The three types of circuits and the operations of the circuits are well known in the art and not described specifically.